CPAP treatment is a common ameliorative treatment for breathing disorders including OSA. CPAP treatment, as described in U.S. Pat. No. 4,944,310, provides pressurised air or other breathable gas to the entrance of a patient's airways at a pressure elevated above atmospheric pressure, typically in the range 3-20 cm H.sub.2 O.
It is known for the level of treatment pressure to vary during a period of treatment accordance with patient need, that form of CPAP being known as automatically adjusting nasal CPAP treatment, as described in U.S. Pat. No. 5,245,995.
NIPPV is another form of treatment for breathing disorders which can involve a relatively higher pressure of gas being provided in the patient mask during the inspiratory phase of respiration and a relatively lower pressure or atmospheric pressure being provided in the patient mask during the expiratory phase of respiration.
In other NIPPV modes the pressure can be made to vary in a complex manner throughout the respiratory cycle. For example, the pressure at the mask during inspiration or expiration can be varied through the period of treatment, as disclosed in the applicant's international PCT patent application No. PCT/AU97/00631.
Typically, the ventilatory assistance for CPAP or NIPPV treatment is delivered to the patient by way of a nasal mask. Alternatively, a mouth mask or full face mask or nasal prongs can be used. In this specification any reference to a mask is to be understood as incorporating a reference to a nasal mask, mouth mask, full face mask or nasal prongs, unless otherwise specifically indicated.
In this specification any reference to CPAP treatment is to be understood as embracing all of the above described forms of ventilatory treatment or assistance.
Breathable gas supply apparatus broadly comprise a flow generator constituted by a continuous source of air or other breathable gas generally in the form of a blower driven by an electric motor. The electric motor driving the blower is typically controlled by a servo-controller under the control of a microcontroller unit. A hospital piped supply can also be used. The gas supply is connected to a conduit or tube, which is in turn connected to a patient mask which incorporates, or has in close proximity, a vent to atmosphere for exhausting exhaled gases.
International PCT patent application No. PCT/AU96/00586 (International Publication No. W0 97/10868) discloses a flow diverting valve with a rotatable control member, see FIGS. 19a and 19b of that application. The valve also has an inlet in fluid communication with a flow generator, an outlet in fluid communication with the patient's airways and a vent in fluid communication with atmosphere. The rotatable control member disclosed can be positioned to close the vent and open a flow path from the valve inlet to the valve outlet for supplying gas during patient inhalation, and throttle or restrict the inlet and open a flow path from the patient to the vent to change the pressure or flow delivered by the circuit to the patient. The valve is thus suitable for use in a CPAP or NIPPV gas supply circuit.
It is an object of the present invention to provide an improved flow control member for a valve and, in a preferred form, a flow control member that allows simplification of an associated closed loop feedback control system and flow rate determination method.